The breaking of water-in-crude emulsions is still a challenge in the petroleum industry. A water-in-oil emulsion results from the mixing of a water-based fluid and crude oil, which are two immiscible fluids. Water or brine typically accompany crude oil during its recovery from a reservoir, and additional water may also be added to aid in secondary oil recovery as the well nears the end of production. At the refinery, additional water may be emulsified into the crude oil in an effort to extract salts and fine solids from the crude oil. The water-based fluid may form droplets within the crude oil, i.e. the water-based fluid droplets are the discontinuous phase, and the oil-based fluid (e.g. crude oil) is the continuous phase.
The presence of the emulsion is beneficial for the extraction process, but it poses major problems for the additional refining steps. The emulsified water may corrode refinery equipment, such as overhead distillation columns, and poison catalysts as a result of dissolved salts. The viscous emulsions can foul machinery, and entrained solids can accumulate in certain unit operations. Crude oil may be lost when trying to dispose or rid the water from the water-in-crude emulsion.
At the oil-water interface of the water-in-oil emulsion, foulants may accumulate and produce a stagnant film that may resist droplet coalescence. The foulants may be or include, but are not limited to, asphaltenes, coke, coke precursors, inorganic solids, and the like. Asphaltenes are most commonly defined as that portion of petroleum, which is soluble in xylene and toluene, but insoluble in heptane or pentane. Asphaltenes exist in crude oil as both soluble species and in the form of colloidal dispersions stabilized by other components in the crude oil. Asphaltenes have higher molecular weights and are the more polar fractions of crude oil, and may precipitate upon pressure, temperature, and compositional changes in crude oil resulting from blending or other mechanical or physicochemical processing.
Asphaltene precipitation and deposition may cause problems in subterranean reservoirs, upstream production facilities, mid-stream transportation facilities, refineries, and fuel blending operations. In petroleum production facilities, asphaltene precipitation and deposition can occur in near wellbore reservoir regions, wells, flowlines, separators, and other equipment. Once deposited, asphaltenes present numerous problems for crude oil producers. For example, asphaltene deposits may plug downhole tubulars, wellbores, choke off pipes and interfere with the functioning of safety shut-off valves, and separator equipment. Asphaltenes have caused problems in refinery processes, such as desalters, distillation preheat units, and cokers.
In addition to carbon and hydrogen in the composition, asphaltenes may contain nitrogen, oxygen and sulfur species, and may also contain metal species such as nickel, vanadium, and iron. Typical asphaltenes are known to have different solubilities in the formation fluid itself or in certain solvents like carbon disulfide or aromatic solvents, such as benzene, toluene, xylene, and the like. However, the asphaltenes are insoluble in solvents like paraffinic compounds, including but not limited to pentane, heptane, octane, etc. Asphaltene stability may even be disturbed by mixing hydrocarbon-based fluids i.e. such as mixing two types of crude oils together, two types of shale oils together, condensates, and others, of different origins at certain ratios as the chemistry of the hydrocarbon-based fluids from different sources may be incompatible and induce destabilization of the asphaltenes therein. In non-limiting examples, such as during refining or fuel blending, two or more hydrocarbon-based fluids may be mixed together. Sometimes, changes in physical conditions are sufficient to induce destabilization, or even the mixture of different hydrocarbon-based fluids that have incompatible chemistries. Said differently, even if neither hydrocarbon-based fluid, alone, has destabilized foulants or the hydrocarbon-based fluid would not act as a destabilizing additive by itself, the mixing or the mixture of two or more hydrocarbon-based fluids may destabilize the foulants present in either hydrocarbon-based fluid.
Coke is an insoluble organic portion of crude oil, distillation residua, or residua from thermal/catalytic conversion processes, such as including but not limited to visbreaker tar or LC finer/H oil residuum. Coke may have polyaromatic hydrocarbons (PAHs) dispersed therein with a ring structure of about 4 to about 5 or more condensed aromatic rings.
Coke precursors are the fragments that make up the coke. They are often formed by thermal cracking, dealkylation and/or dehydrogenation processes commonly used for the breaking down of complex organic molecules. They are barely soluble in the crude oil and/or residual, and tend to precipitate. Once they precipitate, the coke precursors tend to polymerize or conglomerate and form coke.
Inorganic solids may also add emulsion stability if the particle sizes are small enough, e.g. a few microns or less, to become active at the oil-water interface with the resins and asphaltenes from the crude oil. The presence of inorganic solids may add bulk and increase the stability of the asphaltene-resin film at the water-oil interface. There is an inverse relationship between the emulsion stability and inorganic solid particles; a decrease in particle size of the inorganic solids may increase the emulsion stability.
There are large costs associated with shutting down production units because of the fouling components within, as well as the cost to clean the units. The foulants may create an insulating effect within the production unit, reduce the efficiency and/or reactivity, and the like. In either case, reducing the amount of fouling would reduce the cost to produce hydrocarbon fluids and the products derived therefrom. Accordingly, there are large incentives to mitigate fouling during refining.
It would be desirable if better demulsifiers and methods for using the same were developed for separating at least a portion of foulants from the water-in-crude emulsions.